全文获取类型
收费全文 | 24601篇 |
免费 | 857篇 |
国内免费 | 13篇 |
出版年
2020年 | 264篇 |
2019年 | 254篇 |
2018年 | 396篇 |
2017年 | 449篇 |
2016年 | 449篇 |
2015年 | 303篇 |
2014年 | 379篇 |
2013年 | 1910篇 |
2012年 | 752篇 |
2011年 | 761篇 |
2010年 | 477篇 |
2009年 | 459篇 |
2008年 | 650篇 |
2007年 | 655篇 |
2006年 | 564篇 |
2005年 | 508篇 |
2004年 | 495篇 |
2003年 | 442篇 |
2002年 | 500篇 |
2001年 | 766篇 |
2000年 | 791篇 |
1999年 | 584篇 |
1998年 | 269篇 |
1997年 | 231篇 |
1992年 | 460篇 |
1991年 | 419篇 |
1990年 | 467篇 |
1989年 | 435篇 |
1988年 | 410篇 |
1987年 | 418篇 |
1986年 | 423篇 |
1985年 | 436篇 |
1984年 | 351篇 |
1983年 | 312篇 |
1982年 | 241篇 |
1981年 | 221篇 |
1979年 | 408篇 |
1978年 | 284篇 |
1977年 | 259篇 |
1976年 | 233篇 |
1975年 | 355篇 |
1974年 | 392篇 |
1973年 | 363篇 |
1972年 | 339篇 |
1971年 | 298篇 |
1970年 | 278篇 |
1969年 | 328篇 |
1968年 | 372篇 |
1967年 | 329篇 |
1966年 | 333篇 |
排序方式: 共有10000条查询结果,搜索用时 325 毫秒
771.
Juan S. Gómez-Jeria Lic. Q. 《Journal of Near-Death Studies》1993,11(4):219-222
This paper describes a possible near-death experience (NDE) among the Mapuche people of Chile. The individual reporting the experience was in a cataleptic-like state for two days, the experience itself occurring at the end of this period. Some common features of NDEs, such as encounters with deceased people and being sent back, are present, together with clear evidence that past and present cultural environment shape in part the content of mental experiences.This work was funded in part by the University of Chile (DTI Project Q-3064).The author thanks Editorial Andrés Bello for permissionto translate the near death account into English. 相似文献
772.
G. A. Nesvetailov’s 《Knowledge, Technology, and Policy》1993,6(1):38-51
In this paper a method is outlined for measuring the diversity of the results of applied R&D with the use of IPC (International
Patent Classification). The method has been tested in the contexts of the academic physical, engineering, and chemical institutes.
The trend of applied research at a given institute increases both at the level of classes and subclasses, and at the IPC level.
Inventions developed within specializations at each institute have a greater efficiency than other forms of inventive activity.
The objective was to seek the optimal extent of diversification of applied R&D, which would simultaneously ensure the preservation
of the scientific specialization of an institute, the high level of scientific research associated with developing innovations,
and the high overall efficiency of each institute. 相似文献
773.
The purpose of this paper is twofold. First, it provides an historical overview of studies of risk, risk perception, and decision making under risk within the genetic counseling domain. Second, it proposes an alternative conceptualization and operationalization for the study of risk perception. The conceptualization involves probability, adversity, incompleteness, and ambiguity. Prior studies of risk perception focus on the recurrence risk and operationalize risk perception by asking for interpretations of the magnitude of the probability of the outcome. Their focus is on the probability of a particular outcome. We formulate the problem in terms of a gamble and suggest that risk perception be operationalized in terms of the riskiness of the gamble. Our focus is on the riskiness of a decision option which entails two or more outcomes. 相似文献
774.
775.
776.
777.
The crane's foot: The rise of the pedigree in human genetics 总被引:1,自引:1,他引:0
Robert G. Resta 《Journal of genetic counseling》1993,2(4):235-260
The standard pedigree used by geneticists is intimately connected to the history of genetics. Pedigrees drawn today are based on standards established in the early decades of the twentieth century. Those standards were established by geneticists who pursued an active interest in eugenics. The slightly different standards followed in America vs. England to some extent followed the stronger support of Mendelism by the Americans, as well as the individual preferences of the leading human geneticists in those countries. 相似文献
778.
Matthew G. Hile Donna M. Campbell Bagher B. Ghobary Marcie N. Desrochers 《Behavior research methods》1993,25(2):195-198
The development of expert and decision support systems requires the collection, organization, codification, and storage of a body of specialized knowledge. The development, using reconstructive methods, of two such knowledge bases, the first containing the current scientific literature and the second containing an expert’s knowledge, is described for an automated decision support system, the Mental Retardation-Expert. This system provides practitioners with assistance in the treatment of aggressive, self-injurious, and destructive behaviors displayed by individuals with mental retardation or developmental disabilities. The average interobserver reliability of the expert knowledge base ranged from 92.5% to 95.0% when calculated across four clinicians’ assessments of 31 abstracted cases. 相似文献
779.
Numerosity discrimination was examined when items were varied in space-time position rather than in space only. Observers were instructed to indicate which of two adjacent streamsof visual events contained more items. The precision of numerosity discrimination of dynamic events was not remarkably different from that of static patterns. Two basic numerosity biases previously found for static dot patterns—inhibitory overestimation and satellite underestimation—were demonstrated for items distributed randomly over a spatiotemporal interval. It was also demonstrated that two streams, equated in the number and luminous energy of items, are not judged equal in their visible number if items in one of these two streams have longer duration than items in the second stream. These findings can be accounted for by the occupancy model of perceived numerosity (Allik & Tuulmets, 1991a) if it is supposed that the impact that each element has on its neighborhood is spread along both spatial and temporal coordinates. Perceived numerosity decreases with both spatial and temporal proximity between the-visual-items. Space and time have interchangeable effects on perceived numerosity: the amount of numerosity bias caused by the spatial proximity of items can also be produced by the properly chosen temporal proximity of items 相似文献
780.
Checkerboards contain fundamental two-dimensional Fourier components oriented 45° from the edges of individual checks. Previous studies have shown that contingent color aftereffects following adaptation to chromatic checkerboard stimuli were associated with the fundamental components rather than the edges, In the present experiments, we measured contingent color aftereffects, using the method of constant stimuli, after subjects adapted to unfiltered checkerboards and checkerboards with the fundamental Fourier components removed. The adaptation stimuli were magenta (or green) squares and green (or magenta) diamonds; the test stimuli were vertical or oblique sine-wave gratings with different saturations, After adaptation to unfiltered checkerboards, aftereffects contingent on the fundamental components were obtained. In contrast, after adaptation to filtered stimuli, aftereffects of smaller magnitude were found to be aligned with the edges. The data support the previous findings of spatial-frequency-contingent color after-effects with checkerboard adaptation stimuli and indicate that the aftereffects can be associated with edges if the fundamental components of adaptation stimuli are removed by spatial filtering. We reexamined the possibility of color aftereffects induced by imagery of checkerboards. Contrary to the previous reports, no significant aftereffects were obtained. 相似文献